Purpose:
We previously reported bidirectional gene regulation of members of the Bone Morphogenetic Protein (BMP) family (2, 4, & 7) in chick retinal pigment epithelium (RPE) in response to as little as 2 h of imposed optical defocus. This study investigated whether there were also regional differences in the effects of imposed defocus on the expression of these genes in chick RPE.

Methods:
19-day old White-Leghorn chicks wore monocular +10 or -10 D lenses for 2 h. At the end of the treatment period, RPE was isolated and divided into 3 circular zones using punches of 3 and 6 mm radius: central 3 mm zone (T3 or F3; T: treated eyes, F: fellow controls), middle 3-6 mm zone (T6 or F6), and peripheral 6-9 mm circular zone (T9 or F9). RPE RNA was purified and reverse transcribed to cDNA. qPCR was performed to examine the gene expression of BMP2, 4, and 7. Expression levels were compared between lens treated and fellow control eyes. Paired Student’s t test was used for statistical analysis.

Results:
The +10 D lens treatment induced up-regulation of both BMP2 and BMP4 gene expression in the central and middle zones (T3 & T6 regions compared to F3 & F6). For BMP2, gene expression was highly up-regulated, by 129- and 28-fold (T3/F3, n = 3, p = 0.09; T6/F6, n = 4, p = 0.05). The equivalent values for BMP4 gene expression were 13- and 10-fold (T3/F3, n = 3, p < 0.05; T6/F6, n = 4, p < 0.05). BMP7 expression was 3-fold up-regulated for the T3/F3 comparison only. The most peripheral region (T9/F9) did not show differential gene expression between treated and fellows for any of the genes. As expected, the -10 D lens induced down- instead of up-regulation; significant changes were recorded for both BMP2 and BMP4, for both T3/F3 and T6/F6 comparisons. BMP2 was down-regulated by 32- and 12-fold for T3/F3 and T6/F6 comparison, respectively (n = 4), but not for the T9/F9 comparison. Likewise, BMP4 gene expression was down-regulated 12- and 3.6-fold in central (T3/F3) and middle (T6/F6) regions respectively. BMP7 gene expression did not change for any of these three regions.

Conclusions:
This study provides evidence of regional variations in the response of chick RPE to the same defocus, i.e. as imposed by single vision lenses, generally decreasing with increasing eccentricity. The significant up- or down-regulation of BMP gene expression in central RPE points to a critical role of the central retina/RPE in early stage of eye growth regulation.